A liquid crystal display device has been widely used for a display of a personal computer, a television or the like. The device utilizes optical anisotropy, dielectric anisotropy and so forth of a liquid crystal compound. As an operating mode of the liquid crystal display device, such a mode is known as a phase change (PC) mode, a twisted nematic (TN) mode, a super twisted nematic (STN) mode, a bistable twisted nematic (BTN) mode, an electrically controlled birefringence (ECB) mode, an optically compensated bend (OCB) mode, an in-plane switching (IPS) mode, a vertical alignment (VA) mode, a fringe field switching (FFS) mode and a polymer sustained alignment (PSA) mode.
Among the modes, the IPS mode, the FFS mode and the VA mode are known to improve narrowness of a viewing angle, being a disadvantage of the operating mode such as the TN mode and the STN mode. In the liquid crystal display device having the mode of the kind, a liquid crystal composition having a negative dielectric anisotropy is mainly used. In order to further improve characteristics of the liquid crystal display device, a liquid crystal compound contained in the composition preferably has physical properties described in (1) to (8) below.
(1) High stability to heat, light and so forth,
(2) a high clearing point,
(3) low minimum temperature of a liquid crystal phase,
(4) small viscosity (η),
(5) suitable optical anisotropy (Δn),
(6) large negative dielectric anisotropy (Δε),
(7) a suitable elastic constant (K33: bend elastic constant) and
(8) excellent compatibility with other liquid crystal compounds.
An effect of physical properties of the liquid crystal compound on the characteristics of the device is as described below. A compound having the high stability to heat, light and so forth as described in (1) increases a voltage holding ratio of the device. Thus, a service life of the device becomes longer. A compound having the high clearing point as described in (2) extends a temperature range in which the device can be used. A compound having the low minimum temperature of the liquid crystal phase such as a nematic phase and a smectic phase as described in (3), in particular, a compound having the low minimum temperature of the nematic phase, also extends the temperature range in which the device can be used. A compound having the small viscosity as described in (4) decreases a response time of the device.
A compound having the suitable optical anisotropy as described in (5) improves contrast of the device. According to a design of the device, a compound having a large optical anisotropy or a small optical anisotropy, more specifically, a compound having the suitable optical anisotropy is required. When the response time is shortened by decreasing a cell gap of the device, a compound having the large optical anisotropy is suitable. A compound having the large negative dielectric anisotropy as described in (6) decreases a threshold voltage of the device. Thus, an electric power consumption of the device is reduced.
With regard to (7), a compound having a large elastic constant decreases the response time of the device. A compound having a small elastic constant decreases the threshold voltage of the device. Therefore, the suitable elastic constant is required according to the characteristics that are desirably improved. A compound having the excellent compatibility with other liquid crystal compounds as described in (8) is preferred. The reason is because the physical properties of the composition are adjusted by mixing liquid crystal compounds having different physical properties.
As a component of a liquid crystal composition that has a negative dielectric anisotropy and can be used for the liquid crystal display device of the operating mode described above, a number of liquid crystal compounds in which hydrogen on a benzene ring is replaced by fluorine have been studied so far.
For example, compound (A) in which hydrogen on a benzene ring is replaced by fluorine has been studied (see patent literature No. 1). However, the compound has a small optical anisotropy. In addition thereto, compound (B) having alkenyl in which hydrogen on a benzene ring is replaced by fluorine and has been studied (see patent literature No. 2). However, the optical anisotropy of the compound is far from sufficiently large.
Tricyclic compound (C) having an ether-bonding group has been shown (see patent literature No. 3 and Non-patent literature No. 1). In the compound, a range (mesophase range) in which the liquid crystal phase is exhibited is narrow, and the clearing point when the compound is formed into the liquid crystal composition is low.
Tetracyclic compound (D) having an ethylene-bonding group has been shown (see patent literature No. 4). However, in the compound, the dielectric anisotropy is far from sufficiently negatively large and the clearing point when the compound is formed into the liquid crystal composition is low.
Tetracyclic compound (E) having an ether-bonding group and an ethylene-bonding group has been shown (see patent literature No. 5). However, in the compound, the clearing point when the compound is formed into the liquid crystal composition is low.
Tricyclic compound (F) having a butenyl group and an ester-bonding group has been shown (see patent literature No. 6). However, in the compound, the dielectric anisotropy is far from sufficiently negatively large negative dielectric anisotropy, the viscosity is also high, and the clearing point when the composition is formed into the liquid crystal composition is also low.
Thus, the compounds are far from sufficiently suitable for the mode of the liquid crystal display device in recent years.

In a new compound, excellent physical properties that are not found in a conventional compound can be expected. The new compound is expected to have a suitable balance between two physical properties required upon preparing the liquid crystal composition. In view of such a situation, development has been desired for a compound having excellent physical properties and a suitable balance regarding the physical properties with regard to (1) to (8) as described above.